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Percentage Calculator

Use this percentage calculator online to find X% of a number, work out what percent one number is of another, or measure the percentage increase or decrease between two values. Each answer shows the formula with your numbers filled in.

What is X% of Y?

Any number up to ±1,000,000,000,000.

Any number up to ±1,000,000,000,000.

Enter both numbers to see the result and the formula.

How to use the Percentage Calculator

  1. Pick the question you want answered with the Calculation type tabs: X% of Y, X is what % of Y, % Increase or % Decrease.
  2. Type your two numbers into the fields for that tab. Each tab remembers its own numbers, so you can switch back and forth.
  3. Read the result as soon as both fields are filled. The formula underneath shows your numbers substituted in, so you can check the working.
  4. For increase and decrease, watch for the yellow note. If the value moved the other way, it tells you the real direction and which tab to use.
  5. Press Copy result to copy a plain sentence, or Reset to clear every tab.

How the percentage formulas work

A percentage is a number out of 100. Finding X% of Y means scaling Y by X/100. Finding what percent X is of Y means dividing X by Y and multiplying by 100.

Percentage change compares a new value with an original one. The difference is divided by the original value, so the original (A) is the base and can never be zero. The calculator divides by the absolute value of A, so a negative starting value still gives a sensible direction.

Because the base changes, increases and decreases are not mirror images. Going from 80 up to 100 is a 25% increase, but going from 100 back down to 80 is only a 20% decrease.

How to read the result: for X% of Y the answer is a plain number in the same units as Y. For the other three tabs the answer is a percentage. On the Increase and Decrease tabs a positive figure means the value moved in the direction of the tab, and a negative figure means it moved the other way.

Results are rounded to at most 6 decimal places and trailing zeros are dropped, so one third shows as 33.333333 rather than a long string of digits.

X% of Y            = (X / 100) × Y
X is what % of Y   = (X / Y) × 100
% increase (A to B) = ((B - A) / |A|) × 100
% decrease (A to B) = ((A - B) / |A|) × 100
  • To turn a percentage off into a final price, including stacked offers and tax, use the Discount Calculator.
  • If the percentage is a GST rate on an Indian invoice, split it into base amount and tax with the GST Calculator.

Assumptions and limits

  • Results are rounded to 6 decimal places; very small percentages may display as 0.
  • Inputs must be plain numbers (use . as the decimal point; commas are accepted only as thousands separators, so 1,5 is rejected rather than read as 15). Exponent notation such as 1e5 and values beyond ±1,000,000,000,000 are rejected.
  • Percentage change from a starting value of 0 is undefined, so those inputs are rejected.
  • Everything runs in your browser; nothing you type is sent anywhere.

Practical examples

15% of a bill

What is 15% of 2,400? (15 / 100) × 2,400 = 360. Use the X% of Y tab with 15 and 2400.

A test score as a percentage

You scored 42 out of 60. (42 / 60) × 100 = 70%. Use the X is what % of Y tab with 42 and 60.

Up 25%, down 20%

A price rising from 80 to 100 is a 25% increase. The same price falling from 100 back to 80 is a 20% decrease. Enter 200 then 150 on the Increase tab and the calculator reports a 25% decrease and points you to the Decrease tab instead of just showing a minus sign.

Frequently asked questions

How do I calculate a percentage increase between two numbers?

Subtract the original value from the new value, divide by the original value and multiply by 100. From 80 to 100 that is (100 - 80) / 80 x 100 = 25%. Enter 80 as the original value and 100 as the new value on the % Increase tab.

Why does the calculator refuse to use 0 as the original value?

Percentage change divides by the original value, and dividing by zero is undefined. Likewise, you cannot express a number as a percentage of a total of 0. The tool tells you which field to change.

What happens if I use the Increase tab but the value went down?

It still calculates the change and shows it as a negative figure, but adds a note saying the value fell and giving the size of the decrease. For example, 200 to 150 shows -25% and a 25% decrease note.

Is a percentage change the same as a change in percentage points?

No. Moving from 10% to 12% is a rise of 2 percentage points, but as a percentage change it is a 20% increase, because 2 is 20% of 10. This calculator gives the percentage change.

Can I use negative numbers or percentages above 100?

Yes. X can be above 100 or negative in the X% of Y tab, and values can be negative elsewhere. For a negative original value, the change is measured against its absolute value.

How precise are the results?

Results are rounded to 6 decimal places and trailing zeros are trimmed. Inputs are limited to numbers up to 1,000,000,000,000 in size so the arithmetic stays reliable.

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